This invention relates to arrangements for detecting the position of players in a sporting event, and particularly for detecting the occurrence of an "off-side" violation in a soccer game. An off-side condition occurs when the ball is passed to an offensive player who is forward of all defensive players except the goalie. Accordingly, to properly supervise the play of the game, the official must observe players as well as the play of the ball. Determining relative position of players on the field can be difficult because the angle at which the official observes the players will not always coincide with the transverse coordinate of the field. Similar rules concerning the position of players apply in hockey and other games.
Various attempts have been made to provide a system for automatically locating a ball or player on a field. For example, in Brandon et al., U.S. Pat. No. 4,675,816, an electronic tracking system is described wherein a transmitter is located on a ball and a pair of tracking antennas are mounted adjacent the field. The antennas are arranged to track, i.e. point toward the ball and the position of the ball is computed from the pointing angle of the antennas. The Brandon systems requires two antennas to track each object, and it would accordingly require a large number of antennas to track all players on a field. Further, it is not clear that the angular direction-tracking system used by Brandon provides sufficient accuracy.
It is therefore an object of the present invention to provide an improved player/ball tracking system that can simultaneously locate many players on a field and provide assistance to game officials in calling the play of the game.